1. Field of the Invention
This invention relates to a crushing apparatus, and more particularly to an impact type crushing apparatus useful for crushing or grading (chamfering) a raw rough stone such as rock and ore to a desired particle size for the purpose of producing sand. This invention also relates to a crushing method using the above crushing apparatus.
2. Description of the Prior Art
A conventional impact type crushing apparatus is shown in FIGS. 6 to 8, which apparatus is disclosed in Japanese Patent Publication No. 53-33785, for example.
Referring to FIGS. 6 to 8, a rotor 1 is rotatably mounted through a bearing 2 on a vertical shaft. A central distributor 20 is provided at the center of the rotor 1, and each pair of blades 21, 22 and 25 is arranged inside the rotor 1 in such a manner as to be rotated about the central distributor 20. An end blade 24 having a carbide tip 24a is fixed to an end portion of each blade 25, so as to protect the end portion from wear.
The raw rough stone (which will be hereinafter referred to as a charge stock) is supplied from a charge stock supplying device 11 to the central distributor 20, and is then fed by a centrifugal force through the blades 21, 22 and 25 and the end blades 24 to a pair of outlets 19, from which the charge stock is discharged outside the rotor 1.
As shown in FIG. 6, the charge stock discharged is collided against a dead stock 15 (alternatively, a ring liner 16 shown by an alternate long and two short dashed line) formed as a colliding portion inside a housing 8 for accommodating the rotor 1.
In the type where the charge stock is brought into collision against the dead stock 15, the crushing apparatus is employed for grading the charge stock (or correcting a particle shape of the charge stock), while in the type where the charge stock is brought into collision against the ring liner 16, the crushing apparatus is employed for crushing the charge stock.
The blades 21, 22 and 25 in the impact type crushing apparatus are arranged somewhat curvedly in such a manner as to surround the central distributor 20 located at the center of the rotor 1. With this arrangement, the charge stock discharged is accumulated at such a curved portion to form a dead stock 17 until it reaches the end blade 24 through the blades 21, 22 and 25. As a result, an inner wall of the rotor 1 or a base material of the end blade 24 may be protected from wear because of the collision with the charge stock.
As shown in FIG. 8, two outlets 19 are formed at the circumference of the rotor 1, and two units of the blades 21, 22 and 25 as well as the end blade 24 are arranged about 180.degree. apart along the circumference of the rotor 1.
However, the above-mentioned conventional impact type crushing apparatus has the following technical shortcomings.
(1) In the structure shown in FIG. 8 where the end blade 24 is protected by the dead stock 17, the smaller the particle size of the charge stock, the greater the effect of protection in relation with an angle of repose of the particle. However, the charge stock to be actually supplied to the rotor 1 is almost a relatively large particle having a diameter of 20-80 mm. Therefore, when the charge stock is accumulated as a dead stock, the surface of the accumulated charge stock is unstable.
As shown in FIG. 9, the dead stock 17 is repeatedly broken and formed at a local area as shown by a dotted line and an alternate long and two short dashed line. Accordingly, every time the dead stock 17 is broken, the base material of the end blade 24 is exposed at its end portion, and it is therefore worn by the collision with charge stock.
In another type end blade as disclosed in Japanese Utility Model Laid-Open Publication No. 58-73347, the carbide tip is a reversible type where both surfaces of the carbide tip on the center side and the outer circumference side of the rotor may be used, so as to increase life against wear. However, such does not protect the base material of the end blade from wear due to the fluctuation of the dead stock as mentioned above.
In a further of end blade as disclosed in Japanese Patent Laid-Open Publication No. 59-95945, the carbide tip 24a is mounted on a chambered portion of the end blade, and a collision surface of the carbide tip colliding with the charge stock is inclined at about 45 degrees with respect to the center side of the rotor. However, since this angle is greater than an angle of repose (about 40 degrees) of the charge stock (dead stock), a sufficient amount of dead stock is not formed at the end portion of the end blade. As shown by a hatched portion B.sub.1 in FIG. 9, the base material of the end blade 24 is exposed to the charge stock because of the fluctuation of the dead stock 17, causing the generation of wear due to the collision of the charge stock with the base material.
As described above, the prior art impact type crushing apparatus includes the carbide tip mounted at the end portion of the end blade, so as to protect the end portion of the base material of the end blade from wearing due to the collision with the charge stock. However, the base material of the end blade tends to be exposed by the fluctuation of the dead stock, and wear of the base material exposed cannot be prevented.
As shown in FIG. 9, the unstable surface layer of the dead stock is fluctuated in a range of about 1/2 of the particle size r of the charge stock P (between the charge stocks P.sub.1 and P.sub.2). The particle size r is dependent upon a sieve opening size in a sieving step to be conducted prior to the crushing step.
(2) As shown in FIG. 9, the charge stock P shown by a solid line is rolled on the inclined surface of the dead stock 17 and is slid outwardly at the velocity v in the direction shown by an arrow A.
Referring to FIG. 10, as the rotor 1 is rotated at a fixed angular velocity .omega., a constant component (Coriolis' force) 2 mv.omega. is applied to the charge stock P rolling on the inclined surface of the dead stock 17. Referring back to FIG. 9, when the charge stock P reaches the carbide tip 24a of the end blade 24, a frictional force due to the Coriolis' force is generated between the side surface of the carbide tip 24a (end surface 24b of the end blade 24) and the charge stock.
Accordingly, in the end blade 24 having no hard material such as the carbide tip on the end surface 24b as disclosed in the aforementioned prior art, Japanese Patent Laid-Open Publication No. 59-95945, there is formed a large amount of friction as shown by a hatched portion B.sub.2 in FIG. 9 at the end surface 24b by the charge stocks P.sub.3 and P.sub.4 having passed the carbide tip 24a.
Further, in the end blade as disclosed in the aforementioned prior art, Japanese Utility Model Laid-Open Publication No. 58-73347, a hard material is fixed on the entire end surface of the end blade so as to prevent the generation of friction shown by the hatched portion B.sub.2 in FIG. 9. However, the dimension of the hard material in relation to a size (particle size) of the charge stock is not specified.
That is, the length of the surface of the carbide tip on which the charge stock is slid in the radial direction of the rotor must be set to a value such that the influence of the Coriolis' force is reduced to substantially zero, and the charge stock may be retained until the velocity of the charge stock in the radial direction of the rotor is accelerated. However, if the length is too large, the expensive carbide tip is increased in quantity, causing a reduction in economic efficiency.
(3) Particularly in order to solve the problem as mentioned in paragraph (1), it has been attempted to increase the dimension of the carbide tip in the circumferential direction of the rotor and thereby cover the range of the fluctuation of the unstable surface layer of the dead stock. However, the carbide tip is enlarged in size, and bending stress generated by the collision of the charge stock with a bonded portion between the carbide tip and the end blade is increased accordingly.
As a result, there is generated a concentration of stress increased in accordance with the increased size of the carbide tip at the bonded portion between the carbide tip and the end blade, causing damage to the carbide tip or separation thereof from the end blade.